The rapid advancement of multimedia applications requires a system that stores more information more compactly, and is easier to use and handle. Digital video disc (DVD) technology offers this high density format advantage. DVD technology is based on a new generation of a compact disc format which provides for increased storage capacity and performance, especially for video and multimedia applications.
Compact disc (CD) technology has become the global standard for music, entertainment and computer software. Although extremely popular, CD technology has yet been able to provide high density formats. A compact disc (CD) can typically only store approximately five minutes worth of analog image information, and a larger size laser disc of 11.8 inches can store approximately sixty minutes of analog image information. Accordingly, the movie/entertainment and computer industries want to pursue high density formats, such as that found in DVD technology.
As the industry introduces this new digital technology, and other high density optical storage devices, an increasingly important consideration is the beam profile of the pickup head light source and the required focal spot size of the pickup head light source in achieving optimal performance. In general, a high density format disc, such as a DVD disc, has a pit length of 0.4 .mu.m and a track pitch of 0.74 .mu.m, almost half that of a CD format disc. During operation of these high density format discs, data reading applications require 3-4 mW of power, while data writing applications require a minimum of 10 mW to operate. Therefore, when utilizing a single mode optical light source, there is a requirement for operation at a higher power. Typically the focal spot size of a high power spatially multimode output light source is too large to allow for writing data to the high density data storage device. Accordingly, to utilize such high power multimode optical light sources in data writing applications, the focal spot size of the high power light output beam must be reduced in size.
Many light sources can potentially be utilized for these high density read and write applications, such as any type of coherent laser light source, as long as it operates in a donut, high order Hermite-Gaussian mode, or Whispering-Gallery mode. Light sources such as organic lasers, semiconductor lasers, gas lasers, solid state lasers, or higher mode lasers with at least two lobes that are capable of undergoing a phase shift, or other similar light sources can be utilized taking into account the necessary adjustments to reduce the focal spot size. In particular, there is a strong desire to utilize a donut mode vertical cavity surface emitting laser (VCSEL) and/or first order mode light source that has the required high power output, yet in doing so there remains the need to minimize the focal spot size for data writing applications to high density data storage discs.
It would be highly advantageous to remedy the foregoing high power versus focal spot size challenge and other deficiencies inherent in the prior art. Thus, it is highly desirable and an object of the present invention to provide for a light source, more particularly VCSEL capable of generating an optical focal spot size of reduced dimension so as to allow for optimal operation in a data write mode. Accordingly, proposed is a low cost VCSEL with an integrated phase shift mask to be used for high density optical data storage.
Another object of the invention is to provide for a VCSEL having a sufficient output power for data write applications.
It is yet another object of the present invention to provide for a VCSEL that generates a small focal spot size for the writing of information to and from, high density optical storage devices, such as CDs and DVDs.
Still another object of the present invention is to provide for a method of fabricating a VCSEL that allows for high power operation while maintaining reduced focal spot size for use in both optical read and write applications.
Yet another object of the invention is to reduce the complexity, thus cost, of a light source used in a high density optical storage pickup head.